Pulse-modulated traveling wave tube with crossed electric and magnetic fields



Feb. 15, 1955 A. LERBS 2,702,370

PULSE MODULATED TRAVELING WAVE TUBE WITH CROSSED ELECTRIC AND MAGNETIC FIELDS Filed March 16, 1954 2 Sheets-Sheet 1 QSESSE EQSE MODULATOR LERBS TRAVELING WAVE TUBE WITH CROSSED ELECTRIC AND MAGNETIC FIELDS Filed March 15, 1954 Feb. 15, 1955 A.

PULSE-MODULATED 2 Sheets-Sheet 2 /A s w a W E I N L V r L f a s v a a Q a a a m United States Patent Office PULSE-MO DIJ'LATED WAVE TUBE FWITETILTIIJSCROSSED ELECTRIC AND MAGNETIC Alfred- Lerhs, Paris, F'rance, assignor to'Compagnie Generale deTelegraphie Sans Fil, a corporation of France Application 16, 1954,. Serial No. 416,668' Claims priority; application France March 18, 1953 9'Claims. (Cl; 332 -13)' The present invention relates to well-known amplifier, oscillator or multiplier ultra-high frequency tubes, in which an electron beam propagates at right angles with an electric and a magnetic field, the latter fields being perpendicular to each other. The electric fieldis-established between two electrodes which are approximately parallel to the beam, the positive electrode, or anode, being. in the form of adelay line. The twofields are so adjusted that thebeam-velocity' is. equal to the phase velocity of aspace harmonic of an ultra-high frequency wave propagating along'the delayline.

When pulse-modulating the output delivered by such tubes, it would seem: simplest to apply the modulating pulses to the negative one of said two electrodes, so that the electric field should prevail' between the electrodes for the duration ofithesepulsesonly. However, given a constant value of the magnetic field, this type of tube will work properly for one'valuc onlyof. the electric field. it is therefore necessary that the pulses be as perfectly rectangular in shape as'possible. Now, as is Well known, power demand for-'raisingpulse amplitude until crest value is'attained, increases with the gradient. of the pulse flanks. This increases the cost of" the pulse modulating equipment.

It is an object of the present invention: to provide a new embodiment of the above-mentioned tube, particularly suitable impulse-modulation.

It is another objectof. the invention to provide an assembly forpulse modulating the tubeaccording to the invention.

According to" the invention, an auxiliary electrode is provided in the tube, this electrode being" separated from the anode and located opposite the cathode; this electrode is connected to said cathode,- being brought thereby to potential thereof, or abiasing voltage is applied thereto,

bringing it to an even higher negative potential than the cathodewith respect to thexanode', while'rnodulating voltage is applied between the cathode and the auxiliary electrode tobring the latter, for the duration of the modulating pulses, toa" potential approximating anode potential.

According to another embodiment of the invention, a grid is provided between the auxiliary electrode and the cathodethis grid bei'ngbrought, for the duration of the modulating pulses, to a potential intermediate between auxiliary electrode. and cathode potentials.

The invention will behest-understood from the following description and the appended drawing wherein,

Fig. 1 shows a longitudinal section of an amplifier tube according to the invention;

Fig. 2 shows very diagrammatically an end view of the tube shown in Fig. 1;

Figs. 3 to 7 show various embodiments of the electrodes used according to the invention;

Fig. 8 shows an oscillator according to the invention.

Fig. 1 shows schematically a travelling Wave amplifier of rectilinear structure, with crossed electric and magnetic fields. The tube comprises a delay line 2 and a parallel negative electrode 4. Line 2 may for example be brought to a potential equal to the potential of the envelope 1, which in the embodiment shown is grounded. Under these conditions, line 2 may also be grounded as shown at 23. An ultra-high frequency source (not shown) is feeding in the usual way an ultra-high frequency wave to the delay line 2 through the input 6 and the amplified energy is collected at the output 15. A cathode 3, which may for example be brought to a potential equal to that 2,702,370 Patented Feb.= 15, 1955' of electrode-4, is in. the embodiment shown carricdby the latter electrode, although this arrangement is notessential. The cathode is heated by a filament 5,.an extremity of which is connected to the electrode 4. A: magnetic field perpendicular. to the plane of Figure 1 is provided within the tube, for example by a magnet 22 (Fig, 2).

An auxiliary electrode 7, separated from anodev 2,. is located opposite the cathode 3; The modulating voltage is supplied. by asource 9,.through.a transformer 8 whose secondary Winding is connected between electrodes 7- and 4. Electrode. 4 is connected-tothe negative terminal of a highvoltage power. supply source 17, whose positive terminal is grounded. Fil'amentl' is heated by a source 18, through a-transformer 19 whose-secondary winding is connected between electrode 4 and filament 5.

When the tube is not beingmodulated, the electrode 7- is at. cathode potential, since itis connectedto the cathode through the secondary winding of the transformer 8. Whenever the source 9 supplies a pulse, the electrode 7 gainsa positive potential, for instance substantially equalto the-potentialof theanode 2. This results'in thecathodebeing unlocked It will be notedthatthe modulating and bias supply circuitsare independent of each other.

Anyresidual current which could subsist during thepulse'intervals can be substantially eliminated by giving the electrode 7 such a length that it projects beyond the ia thote; 3" in the output direction by a certain amount Further it is obvious that the auxiliary electrode does not need to be of the diagrammatic form shown, butmay be a part of any suitable electronic optical system, as shown in Fig- 4, where-equipotential level lines 21 may be'seen.

In order to still: decrease the residual current through the tubeinthe intervals separating the pulses, or When-nopulses are fed to the-tube, the electrode-7 can be broughtto apot'entiali which is more, negative than that of cathode 3' with respect to theano'deZ, as shown for instance in Fig. 5; According tothis figure, the secondary winding of the transformer 8'isseparated from the negative electrode by a capacitor lil /hose capacitance is-large enough so as not to offer any appreciable impedance to the pulses; Resistor 11, which is in parallel with said secondary winding, is used'for loading the modulator and stabilizing it in operatiom thisresistor of course may be dispensed with. Electrode 7' is brought to a negative voltage with respect to'cathode-3, by'meansof an additional low output-source connected to terminals=20i Accordingato' another feature-of the'invention, the tube may be provided (Fig. 7). Witha grid between the cathode- 3 and the-auxiliary electrode 7'. The grid is brought to a' potential intermediate" between the potentials of these two electrodes'and preferably corresponding to the equip'otential level prevailing in the place occupied by the grid. Moreover, the gri'dshould be of such a shape as to cause minimum: disturbance of the equipotential levels. The grid? whichlis' shown in plan view in Fig. 6, consists of a block l2 supporting parallel rods 13 pointing in the direction ofith'e beam: Such: a grid is easily cooled and easily adaptable: to the tube. In the example shown (-Fig, 7), itiis connecte'd t'o alsuitable'tap on thesecondary Winding of the transformer 8, so that modulation takes place both on the grid 12 and the electrode 7. Furthermore, as an alternative to Figure 7, the grid could be brought to a more negative potential than the cathode D. C. potential.

Figure 8 shows the invention as embodied in the oscillator tube, described in the copending application, Serial Number 281,347, filed on April 9, 1942, and known as Carcinotron, this Word being a registered trade-mark. This tube differs from that shown in Figure 1 in that energy is collected at an output 6 arranged at the end of the line 2 which is nearest to the gun 3. At the other end of the line there is arranged an attenuator 16 which absorbs the spatial components of the ultra-high frequency wave which are propagating in the same direction as the beam. In the embodiment of Fig. 8, cathode 4' is separated from electrode 4". Pulse modulation is applied between the cathode 4' and the auxiliary electrode 7 as in the case of Figure 4. The electrode 4" is brought to a more negative potential than the cathode. In the example shown, an A. C. voltage, supplied by a source 14 through a transformer, is superimposed to the D. C. voltage applied between the delay line 2 and the electrode 4". As a result, the pulse-modulated oscillating energy provided by the tube is also frequency-modulated, since it is known that in this type of Oscillators, frequency is dependent on the potential difference between the delay line 2 and the electrode 4". Any other means could of course be used for the purpose of frequency modulation: for instance the output of the source which feeds the terminals 17 could be varied.

What I claim is:

1. A travelling Wave tube of the type including an anode in the form of a delay line, a negative electrode substantially parallel thereto, means for propagating an ultra-high frequency wave along said delay line, whereby an electric field is provided between said two electrodes, means for providing within said tube a magnetic field normal to said electric field, and a cathode for propagating an electron beam normally to both said fields, said tube comprising: an auxiliary electrode located substantially in front of said cathode and in prolongation of said anode; energized connections for negatively biasing said auxiliary electrode, whereby said cathode is normally blocked; and connections for applying modulating pulses, provided by a modulating source, between said auxiliary electrode and said cathode with positive potential of said pulses applied to said auxiliary electrode for causing said cathode to emit during each of said pulses.

2. A travelling wave tube of the type including an anode in the form of a delay line, a negative electrode substantially parallel thereto, means for propagating an ultra-high frequency wave along said delay line, whereby an electric field is provided between said two electrodes, means for providing within said tube a magnetic field normal to said electric field, and a cathode for propagating an electron beam normally to both said fields, said tube comprising: an auxiliary electrode located substantially in front of said cathode and in prolongation of said anode; energized connections for normally bringing said auxiliary electrode to the same negative potential as said cathode; and connections for applying modulating pulses, provided by a modulating source, between said auxiliary electrode and said cathode for causing said cathode to emit during each of said pulses.

3. A travelling wave tube of the type including an anode in the form of a delay line, a negative electrode substantially parallel thereto, means for propagating an ultra-high frequency wave along said delay line, Whereby an electric field is provided between said two electrodes, means for providing within said tube a magnetic field normal to said electric field, and a cathode for propagating an electron beam normally to both said fields, said tube comprising: an auxiliary electrode located substantially in front of said cathode and in prolongation of said anode; energized connections for bringing said auxiliary electrode to a potential which is negative with respect to said cathode; and connections for applying modulating pulses, provided by a modulating source, between said auxiliary electrode and said cathode for causing said cathode to emit during each of said pulses.

4. A tube according to claim 3 further comprising a grid located between said cathode and said auxiliary ill electrode and a connection for bringing said grid, when modulating pulses are provided, to a potential intermediate between the respective potentials of said auxiliary grid and said cathode.

5. A tube according to claim 4 wherein said grid is constituted by a solid body having fingers extending in the direction of said anode.

7 6. A tube according to claim 1 wherein said auxiliary electrode is extending beyond said cathode in the direction ofthe anode.

7. In combination: a travelling wave tube, of the type including an anode in the form of a delay line, a negative electrode substantially parallel thereto, means for propagating an ultra-high frequency wave along said delay line, whereby an electric field is provided between said two electrodes, means for providing within said tube a magnetic field normal to said electric field, and a cathode for propagating .an electron beam normally to both said fields, said tube further comprising an auxiliary electrode located substantially in front of said cathode and in prolongation of said anode; means for negatively biasing said auxiliary electrode whereby said cathode is normally blocked; and means for applying modulating pulses between said auxiliary electrode and said cathode for causing said cathode to emit during each of said pulses.

8. In combination: a travelling wave tube, of the type including an anode in the form of a delay line, a negative electrode substantially parallel thereto, means for propagating an ultra-high frequency wave along said delay line whereby an electric field is provided between said two electrodes, means for providing within said tube a magnetic field normal to said electric field, and a cathode for propagating an electron beam normally to both said fields, said tube further comprising an auxiliary electrode located substantially in front of said cathode and in prolongation of said anode; a source of direct current potential for negatively biasing said auxiliary electrode whereby said cathode is normally blocked; and a source of modulating pulses, applied between said cathode and said auxiliary electrode, for causing said cathode to emit during each of said pulses.

9. In combination: a travelling wave tube of the type including an anode in the form of a delay line, a negative electrode substantially parallel thereto, means for propagating an ultra-high frequency wave along said delay line, whereby an electric field is provided between said two electrodes, means for providing within said tube a magnetic field normal to said electric field, and a cathode for propagating an electron beam normally to both said fields, said cathode being electrically separated from said negative electrode, an auxiliary electrode located substantially in front of said cathode and in prolongation of said anode; energized connections for negatively biasing said auxiliary electrode whereby said cathode is normally blocked; connections for applying modulating pulses, provided by a modulating source, between said auxiliary electrode and said cathode for causing said cathode to emit during each of said pulses, and means for varying the direct current potential between said negative electrode and said delay line for frequency mgdulating the pulse modulated output energy of the ill 6.

No references cited. 

